The present invention relates, in general, to integrated circuits and, more particularly, to a circuit and method of generating a phase locked loop signal with an offset reference.
Transceiver circuits are used in a myriad of wireless communication applications such as cordless telephones, pagers, cellular telephones, and global positioning systems. The receiver section of the transceiver circuit typically receives a radio frequency (RF) modulation signal from an antenna in a heterodyne system. The receiver includes a mixer that downconverts the RF signal to a lower intermediate frequency (IF) according to a local oscillator signal. Thus, the incoming modulation signal is frequency shifted and modulated data is recovered in the IF signal.
The transmitter section of the transceiver circuit transmits data by modulating a carrier signal having a different frequency than the signal received by the receiver. The transmit signal should have minimum spurious noise transmissions outside the desired bandwidth. Typically, the transmit signal is derived from a low frequency reference signal using a phase locked loop which allows the precise establishment of the transmit frequency. The low reference frequency necessitates the use of large external capacitors in the loop filter to stabilize the generation of the transmit signal.
Accordingly, it would be advantageous to provide an integrated transceiver circuit that generates a transmitter modulated signal that processes high bandwidth information. It would be a further advantage for the transceiver circuit to reduce circuit complexity, cost, and power.